How do I get inside the monastery?

Hint 1 of 10:

You'll need help from someone.

Hint 2 of 10:

Dead souls can be quite helpful.

Hint 3 of 10:

Wear the Ring of Water to get the Will-of-th'Wisps to appear.

Hint 4 of 10:

Then, talk to them and ask them to bring the boat.

Hint 5 of 10:

Follow them in the boat until you reach the tower.

Hint 6 of 10:

That ivy isn't steady enough for you, though.

Hint 7 of 10:

If only you could wait until it grew.

Hint 8 of 10:

You'll have to rely on a bit of magic here.

Hint 9 of 10:

The Druids were very good with magic.

Hint 10 of 10:

Try entering the Druid hand code for ivy.  (It's in the manual.)